Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $146.53   5.232%   $154.1964   $154.20   $154.20   $154.20  
  Purchase #2 $101.94   8.663%   $110.7711   $110.77   $110.75   $110.80  
  Purchase #3 $140.80   10.463%   $155.5319   $155.53   $155.55   $155.50  
  Purchase #4 $26.90   10.775%   $29.7985   $29.80   $29.80   $29.80  
  Purchase #5 $119.82   3.468%   $123.9754   $123.98   $124.00   $124.00  
  Purchase #6 $82.26   12.282%   $92.3632   $92.36   $92.35   $92.40  
  Purchase #7 $87.66   4.504%   $91.6082   $91.61   $91.60   $91.60  
  7 purchase totals = $705.91       $758.2447   $758.25   $758.25   $758.30